Ultraviolet laser-generating device and defect inspection apparatus and method therefor

ABSTRACT

An ultraviolet laser-generating device, for use in a defect inspection apparatus and a method thereof, etc., comprising: a laser ray source for irradiating and emitting a basic wave of laser ray therefrom; a wavelength converter device for receiving the basic wave of laser ray emitted from the laser ray source and for converting it into an ultraviolet laser ray composed of a multiplied high harmonic light of the basic wave of laser ray; and a container having an inlet window, upon which the basic wave of laser ray emitted from the laser ray source is incident upon, and an outlet window for emitting the ultraviolet laser ray composed of the multiplied high harmonic light of the basic wave of laser ray, and installing the wavelength converter device therein, wherein the container is hermetically sealed and is filled up with an inert gas, such as nitrogen or argon gas, therein.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is a continuation of U.S. application Ser. No. 09/764,457,filed Jan. 19, 2001, the subject matter of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an ultraviolet laser-generatingdevice, generating an ultraviolet laser beam or ray to be used forinspection or observation of minute pattern defects, foreign matters,etc., in the fabrications of, such as, semiconductor devices and a flatpanel display, representatively, and further relates to a defectinspection apparatus and a method therefor, with using the ultravioletlaser ray obtained therefrom, thereby enabling detection of defects withhigh resolution, as well as a method for maintenance thereof.

[0004] 2. Description of Prior Art

[0005] For example, circuit patterns formed on the semiconductor devicestends to be fine or minute, more and more, as the technology advance inthe high integration thereof. In particular, masks and reticules, usedin a process of photolithography for manufacturing of the semiconductordevices, as well as the defects of the patterns on a wafer, on whichsuch as the circuit patterns of those are transcribed through exposure,are required to be detected with such the increasing high resolution. Asa method for increasing the resolution, there can be listed up a way ofshortening the wavelength of an illumination light from region ofvisible lights to that of ultraviolet lights. Conventionally, as a lightsource was used or applied, such as a mercury lamp, a Xenon lamp, etc.,and only the light having a required wavelength(s) is/are selectedoptically from the various bright lines (or emission lines) of the lamp,to be applied thereto.

[0006] However, for the bright lines of the lamp, there are problemsthat it is difficult to compensate chromatic aberrations of an opticsystem due to wide range or width of the emission spectrum thereof, andthat the light source comes to be large in size so as to obtainsufficient intensity of illumination, so that it has a bad or lowefficiency, etc. In recent years, an exposure apparatus has beendeveloped, installing a light source, KrF eximer laser of 248 nm inwavelength, as a light source thereof for use in manufacturing of thesemiconductors, however there are also problems that the eximer laserray source comes to be large in size thereof, and that it necessitates acertain countermeasure since it uses a fluorine gas therein, etc.Because of this, as the light source of such the ultraviolet (UV) laserray other than the above-mentioned, YAG laser beam is converted in thewavelength by means of a non-linear optical crystal, thereby obtainingthe third (3^(rd)) high harmonic (355 nm) or the fourth (4^(th)) highharmonic (266 nm) therefrom.

[0007] A wavelength converter device, obtaining the UV laser ray in thismanner is already known by, such as, Japanese Patent Laying-Open No. Hei8-6082 (1996)<prior art 1>, Japanese Patent Laying-Open No. Hei 7-15061(1995) <prior art 2>, Japanese Patent Laying-Open No. Hei 11-64902(1999)<prior art 3>, and Japanese Patent Laying-Open No. Hei 11-87814(1999)<prior art 4>.

[0008] In the prior art 1 is described the wavelength converter device,comprising: resonance means, being positioned at an exit side of a lightemission means for emitting a light having basic wavelength, having aresonance frequency corresponding to a resonance length, which isobtained by setting the length of an optical path, through which thelight propagates, as said the resonance length, and a plural number ofreflection means for reflecting said light in an inside thereof; anon-linear optical material, being positioned on the optical path of thelight propagating through the inside of said resonance means, having ananisotropic property therewith, and for emitting the light beingincident thereupon and at least one light converted in wavelength, beingdifferent from said light in the wavelength thereof; and an electricfield applying means for applying an electric field to said non-linearoptical material, so that the resonance frequency of said resonancemeans is in synchronism with the light of said basic wavelength, therebygenerating the UV laser ray.

[0009] Also, in the prior art 2 is described the wavelength converterdevice, comprising: a light source for supplying a laser ray; an opticalresonator for resonating a laser ray generated from said light source; anon-linear optical material, being positioned within said opticalresonator, for converting the laser ray into a light wave havingwavelength which is shorter than that thereof; and an optical system forfeeding back said laser ray emitted from said optical resonator to saidlight source via the optical resonator, again, wherein said opticalresonator, said non-linear optical material and said optical system aredisposed within a vacuum container.

[0010] Also, in the prior art 3 is described the wavelength converterdevice of an outer resonation type, wherein, in a space defined betweena wavelength converter element (for example, a non-linear opticalcrystal) and an optical member for separation of the laser ray (forexample, a mirror having wavelength selectability therewith) is provideda material, which is optically transparent, or it is filled up with airor inactive gas, etc., or is kept into a substantial vacuum condition,so as to cut off or insulate a portion defined between said wavelengthconverter element and the optical member for separation of the laserbeam, from an outside, thereby preventing dusts and/or gas componentsfrom adhering and/or deposing on a light emission surface for the laserray of said wavelength converter element and/or a light receivingsurface of said optical member for separation of the laser ray.

[0011] And, the prior art 4 also describes an extension or prolongationin lifetime of the laser resonator, by removing contaminating materials,such as oil, etc., adhered on the mirror, which constructs the laserresonator, and/or on the component of the non-linear optical crystal,substantially.

SUMMARY OF THE INVENTION

[0012] However, in the wavelength converter device, a very little amountof active gas, generated when the ultraviolet light is incident upon theoptical members, such as, all of the mirrors, etc., which are providedwithin the optical resonator, or upon the surface of the non-linearoptical crystal, and when it is incident upon suspended or floatingmatters staying behind within the optical resonator, adheres upon thesurfaces of the optical members, such as the mirrors, etc., and/or thenon-linear optical crystal, later, thereby bringing about a problem ofdecreasing the permeability thereof, etc.

[0013] For dissolving such the problems, according to the prior art 2mentioned above, the optical resonator, the non-linear optical materialand the optical system are disposed within the vacuum container.However, since the optical resonator, the non-linear optical materialand the optical system are disposed within the vacuum container,according to the prior art 2, though it is possible to protect theoptical resonator, the non-linear optical material and the opticalsystem from the contamination thereof, it is necessary to make thevacuum container secure so that no deformation due to internal stresswill occur the inside of the optical resonator, the non-linear opticalmaterial and the optical system, as well as to make a seal constructioncertain. As a result thereof, it has a drawback that the vacuumcontainer comes to be complex in the structure thereof, including theseal construction thereof, etc. Further, according to the prior art 2,as described in the Japanese Patent Laying-Open No. Hei 7-15061 (1995),there is a necessity of controlling the increasing temperature of thenon-linear optical crystal, and because of this, heat fills up insidethe vacuum container, therefore it has a drawback of giving an illinfluence upon the optical member(s), such as other mirror(s), etc.

[0014] Also, in the prior art 3 mentioned above, the consideration waspaid onto prevention of the dusts and/or gas components from adheringand/or deposing on the light emission surface of the laser ray of saidwavelength converter element and/or the light receiving surface of saidoptical member for separation of the laser ray, by cutting off theportion defined between the wavelength converter element and the laserbeam separation optical member from the outside, however noconsideration was made upon prevention of adhesion or attaching ofcontaminating materials (contaminants) onto the optical resonator as awhole, including such the non-linear optical crystal, etc.

[0015] As explained in the above, any one of those prior arts 1 to 4pays the consideration upon prevention of adhesion or attaching of thecontaminants onto the optical resonator, as a whole, including thenon-linear optical crystal, etc., with simplified construction thereof,but without receiving the ill influence so much from the control ofincreasing temperature of the non-linear optical element (i.e., thenon-linear optical crystal).

[0016] An object of the present invention is, for dissolving such theproblem(s) as mentioned above, to provide an ultravioletlaser-generating device, being simple in the structure thereof and ableto convert the laser ray entered into with superior efficiency, withpreventing adhesion or attaching of the contaminants on the wholeoptical resonator, including the non-linear optical crystal, etc., butwithout receiving the ill influence so much from the heat generated bythe non-linear optical element, in particular, in the wavelengthconverter thereof, without decrease in intensity of an output of theultraviolet laser ray, while obtaining a long lifetime thereof.

[0017] Also, other object of the present invention is to provide anultraviolet laser-generating device and a maintenance method therefor,wherein an investigation can be made on a cause in the wavelengthconverter, when occurring the decrease in intensity of an output of theultraviolet laser ray, thereby enabling to perform the maintenancethereof with ease.

[0018] Further, other object of the present invention is to provide adefect inspection apparatus and a method thereof, with using such theultraviolet laser-generating device mentioned above, wherein microscopictest pattern formed on an object to be examined, such as thesemiconductor wafer, etc., with an aid of illumination of stableintensity obtained by the ultraviolet laser ray, thereby enabling toexamine the defects in the microscopic test patterns on the test object.

[0019] Also, further other object of the present invention is to providea detect inspection apparatus and a method thereof, for achieving a longlifetime therewith, while can be maintained easily.

[0020] For achieving the above object(s) mentioned in the above,according to the present invention, in the ultraviolet laser-generatingdevice, with paying an attention onto suppression upon potential ofgenerating chemical gas reacted with residual organic matters, byirradiation of the ultraviolet laser ray within an optical resonator ofthe wavelength converter, the optical resonator is so constructed thatno residual organic matter floats therein. In more details, the opticalresonator and the non-linear optical element are provided within acontainer, hermetically, while replacing an inside of the container byan inert gas under the condition of preventing the organic matters fromentering from an outside, so as to provide an environment whereoxidation is reluctant to occur therein, as well as to prevent the heatdue to isothermal control of the non-linear optical element from fillingup therein, thereby preventing the ill influence of the heat upon otheroptical elements.

[0021] Namely, for accomplishing the above object(s), first of all,according to the present invention, there is provided an ultravioletlaser-generating device, comprising:

[0022] a laser ray source for irradiating and emitting a basic wave oflaser ray therefrom;

[0023] a wavelength converter device for receiving the basic wave oflaser ray emitted from said laser ray source and for converting it intoan ultraviolet laser ray composed of a multiplied high harmonic light ofthe basic wave of laser ray; and

[0024] a container having an inlet window, upon which the basic wave oflaser ray emitted from said laser ray source is incident upon, and anoutlet window for emitting the ultraviolet laser ray composed of themultiplied high harmonic light of the basic wave of laser ray, andinstalling said wavelength converter device therein, wherein saidcontainer is filled up with an inert gas therein.

[0025] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, whereinsaid wavelength converter device comprises:

[0026] an optic resonator, being located within said container andconstructed with plural optical members, for resonating the basic waveof laser ray; and

[0027] a non-linear optical element, being located within said containerand constructed with plural optical members, for generating theultraviolet laser ray composed of the multiplied high harmonic lightobtained from the basic wave of laser ray.

[0028] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, whereinsaid container is hermetically sealed, and is further provided withmeans for discharging residual gas within said container and means forsupplying the inert gas into said container.

[0029] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, wherein ona part of inner wall of said container is provided trap means for fixingcontaminants floating within said container thereon.

[0030] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, whereinsaid container, in which said wavelength converter device is installed,is constructed in dual or triple construction, for defining an aperturebetween them, to be filled up with the inert gas therein.

[0031] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, furthercomprising an optical detection means for detecting contaminationcondition within said container.

[0032] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, whereinsaid optical detection means comprises plural number of photoelectricconversion elements positioned within said container.

[0033] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, furthercomprising a detection means for detecting an output intensity of theultraviolet laser ray emitted from said wavelength converter device.

[0034] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, whereinsaid laser ray source comprises a solid-state laser-generating device.

[0035] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, whereinsaid laser ray source comprises a Nd:YAG laser and a wavelengthconverter for converting the laser ray from said Nd:YAG laser into alaser ray having ½ wavelength thereof.

[0036] According to the present invention, for accomplishing the aboveobject(s), there is further provided a defect inspection apparatus fordetecting defects in microscopic patterns formed on a test object, withusing an ultraviolet laser ray, comprising:

[0037] an ultraviolet laser-generating device;

[0038] an illumination optical system for irradiating the ultravioletlaser ray emitted from said ultraviolet laser-generating device upon thetest object;

[0039] an optical system for forming an optical image obtained from saidtest object, being illuminated by said illumination optical system;

[0040] a photoelectric converter for converting the optical image, whichis formed by said optical system, into a signal upon receipt thereof;and

[0041] a defect detection circuit for detecting the defect on said testobject upon basis of the signal obtained from said photoelectricconverter.

[0042] Moreover, according to the present invention, for accomplishingthe above object(s), there is also provided a defect inspectionapparatus for detecting defects in microscopic patterns formed on a testobject, with using an ultraviolet laser ray, comprising:

[0043] a plurality of ultraviolet laser-generating devices, beingaligned so that the ultraviolet laser rays emitted are on a same axis;

[0044] an illumination optical system for irradiating the ultravioletlaser ray(s) emitted from at least one or more of said ultravioletlaser-generating devices upon the test object;

[0045] an optical system for forming an optical image obtained from saidtest object, being illuminated by said illumination optical system;

[0046] a photoelectric converter for converting the optical image, whichis formed by said optical system, into a signal upon receipt thereof;and

[0047] a defect detection circuit for detecting the defect on said testobject upon basis of the signal obtained from said photoelectricconverter.

[0048] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, wherein atleast one of said plurality of ultraviolet laser-generating devices isfor a spare.

[0049] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, whereinsaid illumination optical system comprises an optical system forcombining the ultraviolet laser rays emitted from each of said pluralityof ultraviolet laser-generating devices, to illuminate the test objecttherewith.

[0050] Also, according to the present invention, there is provided theultraviolet laser-generating device, as defined in the above, whereinsaid illumination optical system comprises a coherence reduction opticalsystem.

[0051] Furthermore, according to the present invention, foraccomplishing the above object(s), there is provided a method forinspecting defects in microscopic patterns formed on a test object, withusing an ultraviolet laser ray, comprising the following steps:

[0052] generating an ultraviolet laser ray by the ultravioletlaser-generating device;

[0053] illuminating the test object with using the ultraviolet laser raygenerated by said generating step;

[0054] forming an optical image of the test object from light obtainedin said illumination step of the test object;

[0055] converting the optical image obtained in said forming step into asignal upon receipt thereof; and

[0056] detecting the defect on said test object upon basis of the signalobtained in said converting step.

[0057] Furthermore, according to the present invention, foraccomplishing the above object(s), there is provided a method forinspecting defects in microscopic patterns formed on a test object, withusing an ultraviolet laser ray, comprising the following steps:

[0058] generating a plurality of ultraviolet laser rays, so as to bealigned with on a same axis, as one ultraviolet laser ray;

[0059] illuminating the test object with using the one ultraviolet laserray aligned in ed said generating step;

[0060] forming an optical image of the test object from light obtainedin said illumination step of the test object;

[0061] converting the optical image obtained in said forming step into asignal upon receipt thereof; and

[0062] detecting the defect on said test object upon basis of the signalobtained in said converting step.

[0063] And, according to the present invention, for accomplishing theabove object(s), there is also provided a method for maintaining theultraviolet laser-generating apparatus as defined in the claim 8,comprising the following steps:

[0064] monitoring an output of the output intensity detecting means forcomparing it to a certain value;

[0065] obtaining an output of said optical detection means for detectingcontamination condition within said container of the ultravioletlaser-generating apparatus; and

[0066] determining maintenance of the ultraviolet laser-generatingapparatus, upon basis of an output obtained by said obtaining step.

BRIEF DESCRIPTION OF THE DRAWINGS

[0067]FIG. 1 shows the construction of a defect inspection apparatus asa first embodiment, according to the present invention;

[0068]FIG. 2 shows the outline structure of an ultravioletlaser-generating device, according to the present invention;

[0069]FIG. 3 is a diagram of showing an embodiment of an optical systemfor illumination, including an optical system for reducing coherencetherein, as shown in the FIG. 1;

[0070]FIG. 4 is a perspective view of showing an embodiment of theoptical system for reducing coherence therein;

[0071]FIG. 5 is a front view of the optical system for reducingcoherence therein, which is shown in the FIG. 4;

[0072]FIG. 6 is a perspective view of showing an outlook of a wavelengthconverter, according to the present invention;

[0073]FIG. 7 is a cross-section view of showing a first embodiment ofthe wavelength converter, according to the present invention;

[0074]FIG. 8 is a cross-section view of showing a third embodiment ofthe wavelength converter, according to the present invention;

[0075]FIG. 9 is a cross-section view of showing a second embodiment ofthe wavelength converter, according to the present invention;

[0076]FIG. 10 is a cross-section view of showing a fourth embodiment ofthe wavelength converter, according to the present invention;

[0077]FIG. 11 is the structure view of showing a second embodiment ofthe defect examination apparatus, according to the present invention;

[0078]FIG. 12 is a perspective view of showing another embodiment of theoptical system for reducing coherence therein;

[0079]FIG. 13 is a block diagram of showing the optical system which isshown in the FIG. 12;

[0080] FIGS. 14(a) and (b) are views of showing conditions for zonalillumination (or ring-like illumination), while scanning the ultravioletlaser spot ray on the pupil of an objective lens so as to reduce thespatial coherence therein;

[0081]FIG. 15 is a perspective view of showing an embodiment forreducing the spatial coherence therein by using multi-spots;

[0082] FIGS. 16(a) to (c) are diagrams of showing an optical system forillumination with using the multi-spots;

[0083] FIGS. 17(a) to (c) are views for showing embodiments of anoptical element that forms the multi-spots;

[0084]FIG. 18 is a front view of showing a second embodiment of thedefect examination apparatus, according to the present invention;

[0085] FIGS. 19(a) and (b) are views for explaining light sources of theultraviolet laser beam used in the second embodiment, according to thepresent invention; and

[0086]FIG. 20 is a view for showing luminous flux for slit illuminationused in case of applying a TDI sensor as an image sensor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

[0087] Hereinafter, explanation will be given on embodiments of ahigh-resolution optical system, a defect examining apparatus and amethod thereof, with using such the optical system therein, according tothe present invention, by referring to the attached FIGS. 1 to 20.

[0088] First, explanation will be given on a first embodiment of thedefect examining apparatus according to the present invention. Accordingto the present invention, for the purpose of obtaining high-brightnessillumination in DUV (Deep Ultraviolet) region, a device for emitting anultraviolet laser ray therefrom is applied as a light source (i.e., asource of ultraviolet laser ray) 3. A stage 2 has freedom in thedirections of X, Y, Z and θ, on which as a sample 1 is mounted asemiconductor wafer (an object to be tested: test object), for anexample, on which is formed patterns to be tested (test patterns). Theultraviolet laser ray (DUV laser ray) L2, which is emitted from thesource 3 of ultraviolet laser ray, through a beam expander 6, an opticalsystem 7 provided for the purpose of coherence reduction, a lens 8, apolarization light splitter 9, and a group 10 of polarizer elements, isincident upon an objective lens 11, to be irradiated upon the object tobe tested (for example, the semiconductor wafer: test object) 1, onwhich is formed the test pattern. The beam expander 6 is provided forexpanding the ultraviolet laser ray up to a certain size thereof, and itis in a form of so-called the Koehler illumination, i.e., it isirradiated upon the sample 1 after being condensed in the vicinity ofthe pupil 11 a of the objective lens 11 by means of the lens 8.

[0089] The reflection light, or an optical image obtained from thesample 1 is detected, through the objective lens 11, the group 10 ofpolarizer elements, the polarization light splitter 9 and further animage-forming lens 12, by a image sensor 13, from the upper direction ofthe sample 1. For the image sensor 13, it is necessary to detect the DUVlight and it may be constructed by, such as, a TDI (Time Delayed Image)sensor. In case of applying the TDI sensor as such the image sensor 13,as shown in FIG. 20, it is preferable to construct the lens 8 to includea cylindrical lens 8 therein, so as to bring the luminous flux forillumination upon a slit form 140 fitting to the light receiving surface130 of the TDI sensor, from a view point of an efficiency of theillumination.

[0090] The polarization light splitter 9 has a function of reflectingthe laser ray when the polarization direction thereof is in parallelwith the reflection surface, while penetrating it when that isperpendicular thereto. The ultraviolet laser ray generated by theultraviolet laser ray source 3 is inherently a polarization laser ray,and the polarization light splitter 9 is so positioned that theultraviolet laser ray L2 emitted from the coherence reduction opticalsystem 7 is reflected by the total reflection thereon. The test patternsformed on the test object 1, such as the wafer, in process, show variousshapes or configurations, therefore the reflection light from thepatterns has various polarization directions. The group 10 of polarizerelements, controlling the laser illumination ray and the reflectionlight, has a function of adjusting the rate of polarization in theillumination light, so that the reflection light does not reach upon theimage sensor 13 accompanying with unevenness in brightness due to theshapes of the patterns and the difference in density thereof. Forexample, there are installed a ½ wavelength plate 10 a and ¼ wavelengthplate 10 b for shifting the phase of the illumination light by 45 degreeto 90 degree. Therefore, the light irradiating from the group 10 ofpolarizer elements upon the test object 1 for illumination comes to bethe light that is polarized circularly, and thereafter, all the lightsreflected (or scattered) upon the test object 1, once polarized by thegroup 10 of polarizer elements, are further polarized by 90 degreethereby in the direction of the polarization thereof on the reflectionsurface, then they penetrate through the polarization beam splitter 9.In this manner, since the resolution of the optical system 70 can bechanged depending upon the condition on the illumination, or thecondition on polarization of the detection light. Therefore, it ispossible to improve the performance (i.e., the resolution) of theoptical system 70 through detecting the reflection light, changingdepending upon the density of the circuit patterns formed on the testobject 1, by means of the image sensor 13, while controlling thepolarization condition thereof, by controlling the polarization elements10 a and 10 b to rotate around the optical axes thereof, relatively,upon basis of a spatial image of a plane of pupil of the objective lens11, which is detected by a mirror 86, a lens 87 and a detector 88, asshown in FIG. 11 which will be explained later, for example.

[0091] And, the image sensor 13 is formed by a sensor of, such as anaccumulation type, which can detect the ultraviolet lays (i.e., the TDIsensor), for example, thereby outputting an image signal of light andshade corresponding to the brightness (i.e., the light and shade) ofreflection light from the test patterns which are formed on the testobject 1. Namely, scanning the stage 2 while moving the test object 1 ata constant speed, the image sensor 13 detects information of thebrightness (the light and shade image signal) of the test patterns thatare formed on the test object 1. And the light and shade image signal 13a obtained from the image sensor 13 is inputted into a signal processingcircuit 60, in which the inspection on defects is conducted, includingthe foreign matters in/on the test object. The signal processing circuit60 may be constructed with an A/D converter 14, a gradation converter15, a delay memory 16, a comparator 17, a CPU 19, etc. Further, the A/Dconverter 14 converts the light and shade image signal 13 a obtainedfrom the image sensor 13 into a digital image signal.

[0092] An optical system 71 for focus detection detects the deviation ofthe stage 2 in the Z direction. And, a circuit 72 for focus detection,processing the deviation of the stage 2 in the Z direction detected bythe focus detection system 71, controls driving of deviation of thestage 2 in the Z direction, for example, upon the basis of a drivecontrol instruction from a driver circuit 73 which corresponds to thatprocessing. Due to this, it is possible for the image sensor 13 todetect the brightness information of the test patterns formed on thetest object 1 under the condition of focusing thereupon, with highaccuracy.

[0093] The gradation converter 15 may be constructed with, for example,an eight (8) bit gradation converter, and it treats the gradationconversion, as shown in Japanese Patent Laying-Open No. Hei 8-320294(1996), upon the digital image signal that is outputted from the A/Dconverter 14. Namely, the gradation converter 15 performs conversioninto a logarithm, an exponent, a polynomial, etc., so as to makecompensation for a thin film that is formed on the test object 1, suchas the semiconductor wafer, etc., in process, as well as for theunevenness in brightness of the image produced by interference of thelaser light.

[0094] The delay memory 16 is provided for delaying an output of imagesignal from the gradation converter 15 by the scanning a width of theimage sensor 13, through memorizing it in an amount for one (1) cell,one (1) chip or one (1) shot, which construct the test object 1, such asthe semiconductor wafer, etc.

[0095] The comparator 17 is for comparing the image signal outputtedfrom the gradation converter 15 and the image signal obtained from thedelay memory 16, so as to detect a portion(s) being inconsistent with,as the defect(s). Namely, the comparator 17 compares, in more details,the image delayed by the amount corresponding to a cell pitch, etc.,which is outputted from the delay memory 16, and the detected image.Accordingly, inputting the coordinates, for example, arranged data onthe test object 1, such as the semiconductor wafer, obtainable upon thebasis of design information, with using an input means 18 which may beconstructed with a keyboard, a recording medium, a network, etc., theCPU 19 produces defect inspection data upon basis of the comparisonresult in the comparator 17, so as to store it into a memory device 20.This defect inspection data can be displayed on a display means 21, suchas a display, etc., or may be outputted to an output means 22, therebyenabling observation of a spot(s) of defects through other reviewdevice, etc.

[0096] Further, the details of the comparator 17 may be constructedwith, as shown in Japanese Patent Laying-Open No. Sho 61-212708 (1986),for example, a circuit for adjusting positions on images, a circuit fordetecting difference between the adjusted images, an inconsistencydetector circuit for binary-coding the difference of image, and acharacter extraction circuit for extracting an area, a length,coordinates, etc., from the binary-coded output.

[0097] Next, explanation will be explained on an embodiment of thesource of ultraviolet laser ray (i.e., the ultraviolet laser-generatingdevice). For obtaining high resolution, there is a necessity ofshortening the wavelength of light, and for improving the test speed,the illumination of high brightness. Conventionally, a discharge lamp ofmercury-xenon is used, and it is used widely in the visible region ofthe light emission spectrums (i.e., the emission line spectrums) thatthe lamp generates. However, separating from those light intensities,the emission line spectrums in the ultraviolet and the deep ultravioletregions come up only around several %, comparing to that of the visiblelight (i.e., that in the visible light regions), a large-scaled lightsource is necessary for obtaining a desired brightness with certainty.In case of such the large-scaled light source, there is a limit toseparate it from the optical system for protection from the illinfluence of heat generation thereof. From this viewpoint, according tothe present invention, the ultraviolet laser beam (DUV (DeepUltraviolet) ray) is generated by means of the light source 3. Theultraviolet laser ray indicates the laser ray from 100 nm to 400 nm inwavelength, and the DUV laser ray is the laser ray from 100 nm to 314 inwavelength.

[0098] The ultraviolet laser ray source (the ultravioletlaser-generating device) 3 is constructed with, as shown in FIG. 2, asolid-state laser device (a laser excitation light source) 4 foremitting a basic wave of laser ray of 532 nm in wavelength, and awavelength converter device 5, for example. The solid-state laser device4, penetrating Nd:YAG laser ray of 1064 nm in wavelength through anon-linear optical crystal thereof, so as to obtain a wave doubled infrequency (½ in wavelength), is so controlled that it emits the laserray of 532 nm in wavelength at a constant intensity. Namely, thesolid-state laser device 4 for outputting the doubled wave of the Nd:YAGlaser ray is so constructed that it controls current of a laser powersource depending upon a monitor output, thereby to emit an output of thelaser ray L1 having a constant intensity. The laser ray L1 of wavelength532 nm emitted from the solid-state laser device 4 is in the single modeoscillation, and is incident upon the wavelength converter device 5.

[0099] Also, it does not matter whether the oscillation of thesolid-state laser device 4 as the ultraviolet laser ray source 3 is in acontinuous oscillation mode or in a pulse oscillation mode, however inparticular, in case of detecting the image from the test object 1 whilecontinuously scanning the stage 2, that continuous oscillation ispreferable.

[0100] Also, the ultraviolet laser ray source 3 may be constructed sothat it converts the laser ray of the solid-state YAG laser (1064 nm) bythe non-linear optical crystal, etc., thereby to generate the third(3^(rd)) high harmonic (355 nm) or the fourth (4^(th)) high harmonic(266 nm) of the basic wave thereof. Further, the ultraviolet laser raysource 3 may be constructed with a laser device of generating the laserray having wavelength equal or less than 100 nm.

[0101] Next, explanation will be given on the wavelength converterdevice 5 as an element of the present invention. FIG. 2 is the view ofthe ultraviolet laser ray source 3 in the FIG. 1, seeing from the Zdirection, for showing the outline structure (cross-section) of thewavelength converter device 5. Inside a container of the wavelengthconverter device 5, there are positioned mirrors M1 to M4. Being emittedfrom the solid-state laser-generating device 4 and incident upon atransparent window 35 at an entrance 39 provided on the container 41,the laser ray L1 passes through the mirror M1 and reaches the mirror M2.The mirror M2 penetrates through a part of the incident light, while itreflects the remaining thereof. The laser ray reflected upon the mirrorM2 reaches to the mirror M3. A non-linear optical crystal 30 is disposedon an optical path between the mirror M3 and the mirror M4, and then thelaser ray, being reflected upon the mirror M3 by the total reflection,passes though the non-linear optical crystal 30 to reaches the mirrorM4. And, an optic resonator is constructed with such the opticalmembers, each having high reflectivity, including those mirrors M1 to M4therein. Further, the non-linear optical crystal 30 is disposed at asuitable location that can be calculated optically, therefore by meansof this crystal 30, the incident light is converted into the second(2^(nd)) high harmonic of wavelength having wavelength of 266 nm. Uponthe mirror M4, only the ultraviolet laser ray L2 of the second (2^(nd))high harmonic passes through, therefore it is emitted outside thewavelength converter device 5, via the transparent window 35 at an exit40, which is provided on the container 41. Namely, upon the mirror M4 istreated a coating, which penetrates through the second (2^(nd)) highharmonic but reflects other wavelengths. The laser ray L3 that is notconverted by the non-linear optical crystal 30 is reflected upon themirror M4 to reach the mirror M1, and it follows the same optical pathfor the laser ray L1, again. Herein, a portion of the incident lightpassing through the mirror M2 is detected by a detector means which isnot shown in the figure, to detect the error between the frequency ofthe incident light and the resonance frequency of the wavelengthconverter, thereby bringing both into synchronism with (in a resonatingcondition), always. In more details, by means of a servo-mechanism notshown in the figure (for example, a piezoelectric element, etc.), themirror M3 is moved minutely or finely, so that the length of the opticresonator is controlled with high accuracy. With controlling the lengththereof in this manner, the optical resonator is constructed with theoptical members, each having the high reflectivity, such as the mirrorsM1 to M4. And, with the above-mentioned optic resonator and thenon-linear optical crystal 30, which are provided inside the container41, the wavelength converter 50 is constructed.

[0102] On a while, the ultraviolet laser ray L2 of wavelength 266 nm,which is emitted from the wavelength converter device 5, has coherencetherewith, and it comes to be a cause of generating so-called speckleswhen illuminating the circuit patterns on the test object 1 with usingsuch the laser ray. Accordingly, in the illumination with using such theultraviolet laser ray L2, it is necessary to reduce the coherence. Forreduction of the coherence, it is sufficient to reduce down either oneof the time and spatial coherences thereof. Then, according to thepresent invention, only the special coherence is reduced down by meansof an optical system 7 for reduction of the coherence.

[0103]FIG. 3 is a block diagram for showing an embodiment of anillumination optical system, including the coherence reduction opticalsystem 7 according to the present invention, therein. The laser ray L2emitted from the transparent window 35 at the exit 40 of the wavelengthconverter device 5 is expanded in the beam expander 6 to a parallelluminous flux of a certain size, to be condensed at the focal positionof the lens 24, and thereafter it is condensed upon the pupil 11 a ofthe objective lens 11 through the lenses 25 and 8, and the polarizationbeam splitter 9, as well. However, the focal position 28 of the lens 24is also that of the lens 25 at the same time, therefore the focalposition 28 is in conjugated relation with the position of the pupil 11a of the objective lens 11.

[0104] In the coherence reduction optical system 7, as is shown in FIG.4, for example, a scattering plate 26 of disc form is positioned at thefocal point 28 on the optical path, and is rotated at high speed by amotor 27. Namely, as is shown in FIG. 5, the scattering plate 26, on thesurface of which is machined with appropriate roughness, is positionedat the focal position of the lens 24 (and the lens 25), and the laserspot condensed upon the pupil 11 a of the objective lens 11 is scannedby means of rotation of the motor 27, thereby reducing the coherence, inparticular the spatial coherence thereof. The laser ray is expanded bythe scattering plate 26 to a certain degree, however the lens 25 isselected to have numerical aperture to cover it, and the detailedspecifications of that scattering plate 26 are determined byexperiments. Further, with the coherence reduction optical system 7, themanner for constructing thereof should not be restricted only to theabove-mentioned, but it is also possible to apply a polyhedron rotationmirror, a vibrating rotation mirror, etc.

[0105] By the way, in the laser ray source 3 used for illumination, theultraviolet ray of wavelength 266 nm is obtained by doubling thefrequency of the excitation light L1 of wavelength 532 nm obtained fromthe solid-state laser, with using the mirrors M1 to M4 disposed withinthe container of the wavelength converter device 5 and the non-linearoptical crystal 30 as well, thereby obtaining the ultraviolet light ofwavelength 266 nm. However, as was mentioned previously, the interior ofthe container of the wavelength converter device 5 is very delicate, dueto the fact, for example, that the optical system must be synchronizedwith so that the frequency of the incident light is always in theresonating condition with the resonance frequency of the wavelengthconverter 50, etc. Among those, the non-linear optical crystal 30 hasdeliquescence therewith and is apt to be easily damaged from moisture.Accordingly, for obtaining the ultraviolet laser ray with stability, thesurfaces of the mirrors M1 to M4 and the non-linear optical crystal,which are provided within the optical resonator, must be always kept ina clean condition.

[0106] Also, for obtaining a constant ultraviolet laser ray from thewavelength converter 50 provided within the container of the wavelengthconverter device 5, a thermostatic device (not shown in the figure) isprovided within a slight movement mechanism 45 for supporting thenon-linear optical crystal 30.

[0107] Herein, in case where it is impossible to maintain the interiorof the container of the wavelength converter device 5 in such the cleancondition, the irradiation of the ultraviolet laser ray causes chemicalreactions and the reactant adheres and harden upon the surfaces of theoptical elements, in the inside thereof, thereby bringing about thedecrease of intensity in an output of the ultraviolet laser ray. Then,it is possible to manage by shifting the irradiation position of thelaser ray upon the crystal 30, little by little, when the outputintensity of the ultraviolet laser ray is decreased down, however ittakes a large amount of labor and times.

[0108] Then, first of all, explanation will be given on a firstembodiment of the wavelength converter device 5. In this firstembodiment, as shown in FIGS. 6 and 7, the wavelength converter 50,which is constructed with the optic resonator made with the opticalmembers M1 to M4 and the non-linear optical crystal 30, is shut off orinsulated from the air outside, by means of the container 41, i.e.,within the construction of sealed condition. FIG. 7 shows the conditionof removing a cover 31 therefrom. Namely, the transparent windows 35 arehermetically provided with using, such as an O ring 36, etc., at theinlet 39 and the outlet 40 for the laser ray, which are formed on thecontainer 41. Further, on the container 41 are provided a supply valve32, being provided with a filter 37 at an tip thereof, for supplying agas for use of cleaning, such as an inert gas, from a gas reservoir (notshown in the figure) into the container 41, a discharge valve 33connected to a discharge pump (not shown in the figure) for dischargingresidual gas within the container 41, and a detector 34 for observingthe condition of the gas within the container 41, especially fulfillmentof the inert gas therein. In this manner, the cleaning means forcleaning up the inside of the container 41 is constructed with, forexample, the supply valve 32, connected to the inert gas reservoir (notshown in the figure) and provided the filter 37 at the tip thereof, thedischarge valve 33 connected to the discharge pump, and the detector 34for observing the fulfillment of the inert gas therein. Beingconstructed in this manner, as shown in the FIG. 6, after completion ofthe optical system therein, the container 41 of the wavelength converterdevice 5 is attached with the cover 31 thereon, and the discharge valve33 thereof is connected to the discharge pump not shown in the figure,thereby discharging the residual gas in the container 41. Next, theinert gas is supplied from the supply valve 32 thereinto. The detector34 may be a barometer, for example, for monitoring an atmosphericpressure within the container 41. The inert gas is preferably a gas thatshows no chemical reaction with the laser ray within the wavelengthconverter 50, such as, nitrogen gas, argon gas, etc. Also, the filter 37is provided at the tip of the supply valve 32, and this achievesfunctions of controlling the flow amount of the gas and preventingmixture of impurities therein, when supplying the inert gas through it.

[0109] In particular, under the condition where the residual gas in thecontainer 41 is discharged by connecting the discharge valve (not shownin the figure) to the discharge pump 33, and next the inert gas issupplied from the supply valve 32 into the container 41, to be filled uptherein at around one (1) atmospheric pressure, it is possible to closeup the supply valve 32 and the discharge valve 33, thereby to bring thecontainer 41 into a sealing up condition. And, after filling the inertgas from the supply valve 32 into the container 41 at around the one (1)atmospheric pressure, it is also possible to continue to run the inertgas at a very small amount, so that no fluctuation occurs in the laserray.

[0110] According to the first embodiment mentioned in the above, it ispossible to prevent the mixture of new foreign matters from coming intothe container 41, and as a result, it is possible to maintain thesurfaces of the mirrors M1 to M4 and the crystal 30, which are providedinside the optic resonator, always clean, thereby to prevent them frombringing about decrease of the ultraviolet laser ray in the outputintensity thereof.

[0111] Next, explanation will be given on the second embodiment of thewavelength converter device 5 according to the present invention. Inthis second embodiment, as shown in FIG. 9, the wavelength converter 50is shut off from the air outside, by means of dual structure, includingthe container 42 and a casing (container) 44, i.e., it has the structurein hermetically sealing condition. In the case of this secondembodiment, it is possible to prevent the mechanical stress from beingapplied onto the wavelength converter 50 when closing the cover 31.Namely, on the outer casing 44, the transparent windows 35 arehermetically provided at the inlet 39 and the exit 40 with using, suchas the O-rings 36, etc., and there are provided the valves 32 and 33 forsupplying and discharging the gas and the detector 34 for observing thegas condition within the container. And, the container 42 building upthe wavelength converter 50 therein is supported within the casing 44 bymeans of supporting members 43, thereby constructing the dual structure.

[0112] And, on the inner container 42, there are formed an inlet 46 forentering the incident laser ray through the transparent window 35 at theinlet 39, and an outlet 47 for emitting the ultraviolet laser ray L2 tothe transparent window 35 at the outlet 40, and further are formed airsuction openings 48 and air discharge openings 49 communicating betweenthe inside and the outside of the container 42, as well as pressureopenings 51. In particular, with provision of a large number of such theair suction openings 48 and the air discharge openings 49, being smallin the size, they function as a buffer between the outside of thecontainer 42 and the inside of the casing 44 even when continuing to runthe very small amount of the inert gas, therefore it is possible toremove almost of flow of the inert gas within the container 42, i.e.,remove fluctuation of the laser ray. Of course, under the conditionwhere the residual gas in the container 45, including the container 42,is discharged therefrom by connecting the discharge valve (not shown inthe figure) to the discharge pump 33, and next the inert gas is suppliedfrom the supply valve 32 into the container 45, to be filled up withtherein at around one (1) atmospheric pressure, it is possible to closeup the discharge valve 33 and the supply valve 32, thereby to bring thecontainer 45 into the sealing condition. In this manner, according tothe second embodiment of the wavelength converter device 50, it ispossible to prevent the stress from generating onto the wavelengthconverter 50, and also to prevent the container 42 from mixture of thenew foreign matters, by supplying the inert gas of causing no chemicalreaction with the laser ray, such as the nitrogen gas or argon gas,etc., to be filled up with therein. As a result of this, it is possibleto keep the surfaces of the mirrors M1 to M4 and the crystal 30, whichare provided inside the optic resonator, always in the clean condition,therefore it is possible to prevent them from bringing about thedecrease in the output intensity of ultraviolet laser ray.

[0113] However, according to the second embodiment, the wavelengthconverter 50 is shut off from the air outside by means of the dualstructure of the container 42 and the casing (container) 44, thecontainer may be constructed with triple structure, although it comes tobe complicated a little bit in the structure thereof. With such thetriple structure of the container, since an aperture can be definedbetween the containers as the buffer, it is possible to remove thefluctuation of the laser ray, much more.

[0114] Next, explanation will be given on a third embodiment of thewavelength converter device 5 according to the present invention. Thisthird embodiment, as shown in FIG. 8, is constructed by applying anadhesive or sticky material 38 (a trap means) on an inner wall of thecontainer 41 of the first embodiment. Of course, the third embodimentmay be constructed by applying the adhesive material 38 on an inner wallof the container 42 of the second one. According to this thirdembodiment, it is possible to prevent the foreign matter(s) 39, whichstays within the container 42, from being blown up by wind pressure whensupplying the inert gas therein, to adhere or attach upon the opticalmembers inside. Further, according to this, it is also possible to catchthe floating foreign matter(s) 39 touching on the adhesive material,when discharging the gas within the containers 41 (or 42) outside,thereby to hold it semi-permanently.

[0115] Next, explanation will be given on a fourth embodiment of thewavelength converter device 5, according to the present invention. Inthis fourth embodiment, as shown in FIG. 10, further a plural number ofoptic sensors S1 to S6 are positioned within the container of thewavelength converter device 5, in the third embodiment, and scatteringlight from the contaminant occurring within the container 41 (or 42) isdetected by means of the plural number of the optic sensors S1 to S6,thereby detecting the degree of contamination, or the condition ofcontamination within the containers, in order to observe thecontamination condition on the optical members M1 to M4, and on thenon-linear optical crystal 30 as well. Namely, the plural number ofthose optic sensors S1 to S6 construct an optical contaminant detectingmeans for detecting the scattering light from the contaminant occurringwithin the container 41 (or 42). Since, ordinarily the contaminant ismade of an organic matter, the optic sensors S1 to S6 detect thefluorescence scattering light generated by such the organic matter. And,each of the plural number of the optic sensors S1 to S6 is made from alight condensing lens and a photoelectric conversion element, anddetects the contamination condition upon the surface of the mirror of M1to M4 or the surface of the non-linear optical crystal 30, for example.Since the photoelectric conversion element generates electromotive forcedepending upon an amount of the receiving light thereon, a thresholdvalue is provided for it, and then it can be decided that the surface(s)of the mirror(s) M1 to M4 and/or the surface of the non-linear opticalcrystal 30 is/are contaminated when it exceeds the threshold value. Forexample, it can be decided that the contaminant 40 adheres upon thesurface of the mirror M2 if there is an output signal from the opticsensor S2. Since the wavelength of the laser ray is already known, it ispossible to protect it from an ill influence of an external disturbedlight, by applying the sensors having high sensitivity only a specificwavelength band as those sensors S1 to S6, and it is also possible toset the threshold value for detection to be low. Accordingly, even avery little contaminant can be detected upon the surfaces of the mirrorM1 to M4 and the crystal 30, with high sensitivity. Monitoring theoutput of the ultraviolet laser ray L2 emitted from the wavelengthconverter device 5 by a detector means 100, which is constructed withthe photoelectric conversion elements, etc., and which is providedseparate from the optic path of the illumination light, an alarm can begiven, for example, when decrease is found in the intensity thereof (forexample, when it comes down to around 50% of an initial value), then thesensors S1 to S6 are determined by each, whether the output signal ofwhich exceeds a threshold value predetermined for it or not. With this,a portion(s) which is/are contaminated with the contaminant(s) upon thesurface(s) thereof can be specified or identified among the opticalmembers, i.e., the mirrors M1 to M4 and the crystal 30. Then, theoptical member(s), being determined contaminated, will be treated withcleaning upon the surface thereof, or will be replaced with a new orother optic member that in not contaminated.

[0116] However, as another method for monitoring the ultraviolet laserray L2 emitted from the wavelength converter device 5, an output of thebeam expander 6 or the coherence reduction optical system 7 may bemonitored. Of course, when monitoring the output of the beam expander 6or the coherence reduction optical system 7, the decrease in the outputintensity due to the contamination of the optical system 6 or 7 isincluded into the output to be monitored.

[0117] Also, in a case where no output signal is produced from the opticsensors S1 to S6, and where the output intensity is reduced in theultraviolet laser ray L2, which is emitted from the wavelength converterdevice 5, when monitoring it by the detection means as was mentioned inthe above, the cause may be considered to lie in the non-linear opticalcrystal 30. In this case, a possibility is high that the inside ofcrystal 30 burns out upon the irradiation of the laser ray, thereforethe non-linear optical crystal 30 may be adjusted to be shifted in the Yand Z directions by means of the slight movement mechanism 45, so thatthe ultraviolet laser ray L2 can be increased in the output intensity.Of course, the present fourth embodiment can be applied to the secondembodiment shown in the FIG. 9, too.

[0118] As was explained in the above, with monitoring the contaminationcondition within the wavelength converter device, it is possible to makethe determination upon the necessity of maintenance in the wavelengthconverter device, with ease and appropriateness, and as a result, it ispossible to remove consumption of unnecessary or needless time paid foradjusting the optical system within the wavelength converter devicewithout reasons.

[0119] According to the embodiments of the present invention mentionedin the above, it is possible to obtain a source of laser ray of a longlife-time, without decrease of output intensity in the ultraviolet laserray, i.e., stable oscillation of the ultraviolet laser ray for a longtime period, by elongating the life-time of the wavelength converter. Asa result of this, it is also possible to detect the microscopic patternsformed on the test object 1 with high resolution, thereby to examinethose defects occurring in the microscopic patters with highreliability.

[0120] Next, a second embodiment of the detect examination apparatus,according to the present invention, will be explained by referring toFIGS. 11, 18 and 19. In this second embodiment, the difference from thefirst embodiment shown in the FIG. 1 lies in that, at first, as shown inFIGS. 19(a) and (b), the ultraviolet laser ray source (the ultravioletlaser-generating device) 3, each comprising the solid-state laser device(the laser exciting light source) 4 and the wavelength converter device5, is provided in a plural number thereof so that the ultraviolet laserrays emitted from those ultraviolet laser ray sources 3 are on the sameaxle, and therefore as shown in the FIG. 19(b), they can be used byoscillating only one of them for exchanging it by the other(s) when theone is in trouble, or as shown in the FIG. 19(a), all of them areoscillated while operating each at the low output. Namely, in the secondembodiment, the plural number of the ultraviolet laser ray sources 3 a,3 b and 3 c, each comprising the solid-state laser device 4 and thewavelength converter device 5 therein, are provided, and mirrors 81 a,81 b and 81 c are so constructed that the ultraviolet laser rays emittedfrom those ultraviolet laser ray sources 3 a, 3 b and 3 c are reflectedupon them on the same axle in a direction, such as of Z, so as to beinputted into the beam expander 6. In particular, as shown in the FIG.19(b), selecting each of the mirrors 81 a to 81 c (a selection opticalsystem) by exchanging (or shifting) thereof, it is possible to selectthe output(s) of the ultraviolet laser ray sources 3 a to 3 c. Withthis, it is possible to make the ultraviolet laser ray sources providedfor spares emit the normal ultraviolet laser rays always, so as toirradiate upon the test object 1, to detect the microscopic patternsformed on that test object 1 with high resolution, and to detect thedefects occurring in those microscopic patterns with high reliability.In this manner, even during a period when they are operating normally asthe laser ray sources, it is possible to make adjustment on thewavelength converter device(s) 5 among them, being abnormal as theultraviolet laser ray source, being broken or deteriorated therein, orto replace it/them by a normal wavelength converter device(s) 5 in placethereof.

[0121] However, as was shown in the FIG. 19(a), in a case where theultraviolet laser rays emitted from the plural number of the ultravioletlaser ray sources 3 a to 3 c are applied upon a combining optical systemof 81 a to 81 c to be combined with, it is possible to adjust an outputautomatically, by monitoring the output as a whole by, such as a TVcamera 85, so that the current value is adjusted, for example, to besupplied to the solid-state laser device 4, which is included in thenormal ultraviolet laser ray source(s) other than the deteriorated one,to increase the output thereof, thereby obtaining the monitored outputas a whole at a predetermined value. And, for the wavelength converterdevice 5 of the deteriorated ultraviolet laser ray source, it is alsopossible to adjust the output intensity of the ultraviolet laser ray L2so as to increase, through shifting the non-linear optical crystal 30 inthe Y and Z directions by means of the slight movement mechanism 45.

[0122] Further, as shown in the FIG. 18, with positioning theultraviolet laser ray source 3 comprising plural light sources 3 a and 3b separate from the optical system 70, it is so constructed thatpropagation of mechanical vibration generated by the stage, etc., andtransmission of heat can be shut off from the ultraviolet laser raysource 3 to the optical system 7'Further, according to the presentembodiment shown in the FIG. 18, the ultraviolet laser ray source 3 isprovided under a base 80 for removing vibration. In this case, it isconstructed to make exhaustion of the air locally, so that, not shown inthe figure, the heat generated by the ultraviolet laser ray source 3will not transmitted up to the upper portion of the base 80. The laserrays L2, each being emitted from the respective ultraviolet laser raysources 3 a to 3 c, are reflected into the direction Z upon the mirrors81 a to 81 c, respectively, and reach to the optical system 70 through amirror 90 and the beam expander 6. In the pattern inspection thereof,the examination is conducted upon the whole surface of the semiconductorwafer 1 by scanning the stage 2, on which the wafer 1 is mounted, intothe X and Y directions, however since the position of center of gravityof the stage is shifted accompanying with the movement thereof, the base80 is inclined. In this case, the base 80 is turned back to thehorizontal condition by means of an air turbo, etc., however since theultraviolet laser ray L2 emitted from the ultraviolet laser ray source 3is equal or less than 1 mm in a beam diameter, it can be expected thatthe optical axis of the optical system 70 comes out of that of theultraviolet laser ray L2, temporally. Because of this, according to thepresent invention, the mirror 90, the lens 91, and a position detector90 as well, are provided on the base 80, thereby detecting a shiftamount of the ultraviolet laser ray L2, so as to shift the mirror 81 byan actuator, such as a piezoelectric element, etc., and to correct theoptical path of the ultraviolet laser ray L2 being out of the axisthereof, at high speed. Herein, on the mirror 90 is coated a reflectionfilm so as to reflect a little amount of light of the ultraviolet laserray L2, and the lens 91 is provided for extensively projecting thisreflection light upon the position detector 92. The position detector 92is constructed by, for example, positioning a light receiving element tobe dividing into the X and Y directions, thereby to detect the shiftamount of the laser ray through calculation of detection signals ofthose light receiving elements, by means of an electric circuit notshown in the figure. With this, it is possible to make the ultravioletlaser ray emitted from each of the ultraviolet laser ray source 3 a and3 b to be incident upon the optical system 70, with stability.

[0123] As was explained in the above, with provision of the pluralnumber of the ultraviolet laser ray sources 3, each comprising thesolid-state laser device 4 and the wavelength converter device 5therein, it is possible to selectively change the output of theultraviolet laser ray, and as a result of this, it is possible to obtainthe normal ultraviolet laser ray source, always with certainty, and toperform the inspection of the microscopic patterns by using theultraviolet laser ray, with continuity and high reliability.

[0124] Next, explanation will be given on another embodiment of thecoherence reduction optical system 7. In this embodiment, as shown inFIG. 12, the laser ray is scanned in two-dimensional manner by means ofa pupil scanning mechanism, which is constructed with two (2) pieces oforthogonal scanning mirrors 61 and 64, thereby being reduced in thecoherence thereof, spatially. FIG. 13 is a diagram of the illuminationsystem. The ultraviolet laser ray L2, being emitted from the ultravioletlaser ray source 3 and expanded to a certain size by the beam expander6, comes to be a parallel luminous flux to be reflected upon the mirror61 and to be condensed by the lens 62, and thereafter it comes to be aparallel luminous flux, again, through the lens 63 to be condensed uponthe pupil 11 a of the objective lens 11 by the lens 8. Referencenumerals 67 and 69 indicate the reflection positions of the laser lightupon the scanning mirrors 61 and 64, and they are in the conjugatedrelationship with the surface of the test object 1 in the positionsthereof. Also, a reference numeral 68 is a surface of a first pupil,being in the conjugated relationship with the pupil 11 a of theobjective lens 11. Accordingly, through rotational or wobbling controlof the scanning mirrors 61 and 64 by means of electric signals, it ispossible to scan the ultraviolet laser ray L2 upon the pupil 11 a of theobjective lens 11, in the two-dimensional manner. The electric signal tobe inputted to the scanning mirror 61 or 64 may be a triangle signal ora rectangular signal, etc., for example, and the scanning of theultraviolet laser ray can be conducted in various shapes, by changingthe frequency and/or amplitude of that electric signal. In particular,scanning the ultraviolet laser spot upon the pupil 11 a of the objectivelens 11 in a zonal (or ring-belt like) manner, as shown in FIGS. 14(a)and (b), by controlling the scanning of the scanning mirrors 61 and 64,respectively, it is possible to perform a zonal illumination through theobjective lens 11 upon the test object 1, while reducing the coherencethereof. Further, as will be mentioned later, even in a case that theillumination light is an ultraviolet multi-slit spot beam correspondingto the TDI sensor, it is also possible to remove the opticalinterference, completely, by positioning the scattering plate after thepupil scanning mechanism which is constructed with the scanning mirrors61 and 64 mentioned above.

[0125] By the way, on the optical path of the illumination light, amirror 82 is positioned for dividing an amount of illumination light sothat it does not impedes the illumination of the test object 1, and itis constructed so that a portion of the illumination laser ray dividedby the mirror 82 mentioned above can be observed by means of the TVcamera 85. Namely, the light divided by the mirror 82 mentioned above isthe ultraviolet laser ray, therefore a screen 83, which emitsfluorescence light when that ultraviolet laser ray is incidentthereupon, is provided at the position in the conjugated relationshipwith the pupil 11 a of the objective lens 11. As a result of this,expanding the fluorescence light image 92 occurring upon the screen 83(in the case where the ultraviolet laser ray is scanned in the zonalmanner, two-dimensionally) through a lens 84, it is possible to observesuch the image 91, as shown in FIG. 14(a), through the TV camera 85.Further, a numeral reference 93 indicates an outer diameter of the pupil11 a of the objective lens 11. And, processing the image 91 outputtedfrom the TV camera 85 in a signal processing circuit 60 shown in theFIG. 18, it is possible to obtain an amount of shifting of theillumination light 92 from the center of the pupil 11 a, for example,and this shift amount is fed back to a controller circuit 95, therebyenabling control of the scanning by means of the scanning mirrors 61 and64 of the coherence reducing optical system 7.

[0126] Also, the signal processing circuit 60, encoding the imagereceived by the TV camera 85 into binary values, obtains an area of theillumination by adding up pixels being brighter than a certain valuethereof, thereby enabling optimization of an illumination condition(i.e., the illumination σ).

[0127] Further, it is needless to say that the scanning of theultraviolet laser ray by means of the scanning mirrors 61 and 64 isconducted during the storage time of the image sensor 13.

[0128] Next, explanation will be given on another embodiment in relationto the condition of illumination. Namely, in this embodiment, theultraviolet laser ray is irradiated upon the pupil 11 a of the objectivelens 11, for multi-spot illumination. Since the illumination σ can begained by conducting the multi-spot illumination in this manner, it ispossible to delay the scanning time by means of the scanning mirrors 61and 64. FIG. 15 is a three-dimensional view of the coherence reducingoptical system 7, in which a multi-lens array 65 and a lens 66 aredisposed, and FIG. 16 is a diagram of an illumination system using ittherein. Namely, the multi-lens array 65 and a lens 66 are added inrelation to the incident ultraviolet laser ray L2, thereby making upimaginary multiple sources of the ultraviolet laser rays, and they arecondensed upon the pupil 11 a of the objective lens 11. Further, areference numeral 110 shown in FIG. 16(a) indicates a mask for formingthe multi-spotlights, in more preferable manner. Also, a referencenumeral 110 a shown in FIG. 16(b) is a front view of an example of themask for forming the multi-spotlights, and a reference numeral 110 bshown in FIG. 16(c) a front view of another example of the mask forforming the multi-spotlights. Reference numerals 112 a and 112 bindicate portions for penetrating the light therethrough, while 111 aand 111 b portions of shutting off the light. As for the means (i.e.,the multi-lens array) 65 for making up the imaginary multiple sources ofthe ultraviolet laser rays, it can be obtained by lens arrays, in whichtwo (2) cylindrical (or renticular) lens arrays 113 are positioned withcrossing at right angle, for example, as shown in FIG. 17(a), or bypositioning a rod-lens array 115 of disposing small-sized convex lensestwo-dimensionally thereon, as shown in FIG. 17(b). However, in a casewhere the storage type TDI sensor is used as the image sensor, it isnecessary to make the multi-spotlights into multi-slit spotlights 140,corresponding to the light receiving surface of the TDI sensor (forexample, as was shown in the FIG. 20). For that purpose, as such themeans 65 mentioned above, a long and narrow rod-lens array 116, shown inFIG. 17(c), for example, might be used therefor.

[0129] And, FIG. 14(b) shows the scanning condition by themulti-spotlights, which comes to be the zonal illumination upon thepupil 11 a of the objective lens 11. In the same manner, the scanning isconducted upon the pupil 11 a of the objective lens 11, by themulti-slit spotlights corresponding to the TDI sensor. A pitch 120between the points of condensing the laser rays upon the pupil 11 a ofthe objective lens 11 can be changed freely, by changing the focaldistance of the lens 66, as well as the focal distance(s) of the otherlens(es).

[0130] According to the present invention, it is possible to achieve aneffect of providing the ultraviolet laser-generating device; wherein thewavelength converter device does not receives the ill influence largely,from the heat generated by the non-linear optical elements, and thecontaminants can be prevented from adhering upon the optic resonator, asa whole, including the non-linear optical elements therein, with suchthe simple construction, thereby converting the incident laser ray inthe wavelength with high efficiency, and obtaining the long life-timethereof, without reducing the output intensity of the ultraviolet laserray, as well.

[0131] Also, according to the present invention, it is possible toachieve an effect that, when the decrease of output intensity in theultraviolet laser ray occurs in the wavelength converter device, theinvestigation of the cause thereof, and the maintenances, including thedetermination of the necessity thereof, can be performed, easily.

[0132] Further, according to the present invention, it is also possibleto achieve an effect that the detection and/or the inspection of defectsin the microscopic test patterns, which are formed on the test object,such as the semiconductor wafer, etc., can be achieved, with highresolution and high reliability, through the illumination of theultraviolet laser ray with stable intensity thereof.

What is claimed is:
 1. An ultraviolet laser-generating device,comprising: a laser ray source for irradiating and emitting a basic waveof laser ray therefrom; a wavelength converter device for receiving thebasic wave of laser ray emitted from said laser ray source and forconverting it into an ultraviolet laser ray composed of a multipliedhigh harmonic light of the basic wave of laser ray; and a containerhaving an inlet window, upon which the basic wave of laser ray emittedfrom said laser ray source is incident upon, and an outlet window foremitting the ultraviolet laser ray composed of the multiplied highharmonic light of the basic wave of laser ray, and installing saidwavelength converter device therein, wherein said container is filled upwith an inert gas therein.
 2. A defect inspection apparatus fordetecting defects in microscopic patterns formed on a test object, withusing an ultraviolet laser ray, comprising: a plurality of ultravioletlaser-generating devices, being aligned so that the ultraviolet laserrays emitted are on a same axis; an illumination optical system forirradiating the ultraviolet laser ray(s) emitted from at least one ormore of said ultraviolet laser-generating devices upon the test object;an optical system for forming an optical image obtained from said testobject, being illuminated by said illumination optical system; aphotoelectric converter for converting the optical image, which isformed by said optical system, into a signal upon receipt thereof; and adefect detection circuit for detecting the defect on said test objectupon basis of the signal obtained from said photoelectric converter. 3.A method for inspecting defects in microscopic patterns formed on a testobject, with using an ultraviolet laser ray, comprising the followingsteps: generating an ultraviolet laser ray by the ultravioletlaser-generating device, as defined in the claim 1; illuminating thetest object with using the ultraviolet laser ray generated by saidgenerating step; forming an optical image of the test object from lightobtained in said illumination step of the test object; converting theoptical image obtained in said forming step into a signal upon receiptthereof; and detecting the defect on said test object upon basis of thesignal obtained in said converting step.